Εικόνες σελίδας
PDF
Ηλεκτρ. έκδοση

PER CENT OF WATER OF CRYSTALLIZATION. 29

d. Weigh an evaporating dish or a watch glass carefully, and then weigh into it accurately about 5 grams anhydrous calcium chloride. Let stand at least twenty-four hours, Results? Record the weighings as in b.

and weigh again.

What do these substances absorb from the air?

EXPERIMENT XIX.

PER CENT OF WATER OF CRYSTALLIZATION.

Apparatus. Evaporating dish, balances, wire gauze, ring stand.

Materials.

Powdered gypsum (not plaster of Paris), chemi

cally pure barium chloride (the hydrate).

a. Weigh your evaporating dish (be sure it is clean and dry), and into it weigh accurately about 3 grams of finely powdered gypsum. Get the exact weight of the gypsum taken, and record it.

Then

b. Heat the evaporating dish on a clean wire gauze for ten minutes with the hottest Bunsen flame. let the dish cool, weigh it, and record the result. Now heat the dish again for five minutes, let it cool, and determine the weight. Continue until you have "constant weight."

c. Record your results thus:—

[merged small][ocr errors][ocr errors][merged small][merged small][merged small][ocr errors][merged small][ocr errors][merged small][ocr errors][merged small]

d. Weigh into the evaporating dish, accurately, about 3 grams of pure, powdered barium chloride. Place the evaporating dish on a wire gauze about 4 inches (1 dm.) above the top of a Bunsen flame. Heat the dish for ten minutes, then let it cool, and weigh it. Heat it again, to constant weight. Record the results as in c, and calculate the per cent of water driven off.

EXPERIMENT XX.

DEFINITE PROPORTIONS.

Apparatus. Evaporating dishes, beaker, balances, watch glass. Materials.

Sodium bicarbonate, dilute hydrochloric acid.

a. Weigh your evaporating dish carefully, and then weigh into it accurately about 5 grams of sodium bicarbonate. Transfer the bicarbonate without loss to a beaker covered with a watch glass; then add the dilute hydrochloric acid a little at a time. When adding acid draw the watch glass a little to one side; at other times let it cover the beaker.

b. The effervescence (foaming) is due to the escape of carbon dioxide gas. When all the solid has dissolved, add a drop or two more of the acid, to be sure no bicarbonate remains; then pour the solution into the weighed evaporating dish. With 5 c.c. water, wash what has spattered on the watch glass into the beaker, and with this water rinse what adheres to the beaker into the evaporating dish. Rinse the beaker with 5 c.c. more water, and add the rinsings to the evaporating dish.

DEFINITE PROPORTIONS.

31

c. Evaporate the solution to dryness, on a water bath or a steam bath, if possible; otherwise, on a wire gauze. If you use wire gauze take great care to avoid spattering either the solution or the solid which remains after the water has boiled away. If considerable spattering begins, remove the flame for a moment and let the dish cool; then apply the flame again gently. Keep flame in constant motion at the end of the process.

When the solid in the dish is perfectly dry, let the dish cool to the temperature of the room. Then weigh it accurately. Heat to constant weight.

d. Record your results thus:

[merged small][merged small][merged small][ocr errors][ocr errors][ocr errors][ocr errors][merged small]

.. Wt. of bicarbonate used

Wt. of evaporating dish + sodium chloride

[ocr errors][ocr errors][ocr errors][ocr errors][merged small][merged small]

Get the simplest ratio between the amount of bicarbonate taken and that of sodium chloride obtained as follows:

Wt. of bicarbonate: Wt. of sodium chloride :: 1: x.

Calculate the value of x to two decimal places. x =? e. Repeat the preceding operations, weighing out accurately about 8 grams sodium bicarbonate. If the volume of the solution is too great to go into the evaporating dish all at once, evaporate part of the water and then add the remainder of the solution. Be sure to rinse.

Calculate the ratio between sodium bicarbonate and sodium chloride as before. Compare the ratios. Conclusion?

EXPERIMENT XXI.

CHLORINE.

Caution. Avoid inhaling much chlorine. If you have inhaled it, smell ammonia cautiously. If the gas gets into the room, sprinkle a few drops of ammonia water upon your table.

Apparatus. 100 c.c. flask, ring stand, wire gauze, one-holed stopper, two right-angled tubes (one with long arm), rubber connector, collecting bottle, test tubes, perforated cardboard

cover.

[ocr errors]

Materials. Manganese dioxide (in lumps), concentrated hydrochloric acid, white paper, red cheese cloth, litmus solution, indigo solution, potassium chlorate, ink, printed paper.

a. Support a 100 c.c. flask on a wire gauze in a ring stand. The flask is provided with a one-holed stopper and a delivery tube bent twice at right angles. The double bend is produced by joining two right-angle tubes by means of a rubber connector. The second right-angle tube is turned down; its end should be 2 to 3 cm. above the table.

b. Put into the flask half a test tube of manganese dioxide in small lumps, add 20 c.c. concentrated hydrochloric acid, and attach stopper and delivery tube.

Warm the flask gently, and fill a dry bottle, turned mouth up, with the resulting chlorine gas. While the bottle is being filled keep it covered with a piece of card

[blocks in formation]

board; the cardboard has a hole for the delivery tube. You may know when the bottle is full by the rise of chlorine to the top; white paper held behind the bottle will help you.

c. Stopper the bottle when it is full, and fill two dry test tubes with the gas. Then pass the gas for five minutes into 15 c.c. cold water in a test tube. This gives chlorine water.

When you are through, disconnect the apparatus at once, and wash the remaining manganese dioxide twice with water.

d. What is the color of the gas? Apply a lighted match to a test tube of it. Does the gas burn? Support com-bustion?

e. Put into the bottle of the gas a small piece (2 cm. square) of dry red cheese cloth, a wet piece of the same, a piece of paper containing print, and a paper with ink marks. Leave ten to fifteen minutes. Results?

f. Put 5 c.c. of the solution of chlorine made in c upon 1 sq. cm. of the colored cloth in a test tube. Upon paper with both print and ink marks on it. Results? What seems to be necessary in order that chlorine may bleach?

g. Into a test tube of the gas pour 5 c.c. cold water, close the mouth of the test tube tightly with the thumb, and shake vigorously. Remove thumb under water. Result? Explain.

h. To 1 c.c. dilute litmus solution, add chlorine water until you get a decided change. Explain result. Repeat, using indigo solution instead of litmus. Result?

i. An easy way to make a solution of chlorine is to treat about 1 gram of potassium chlorate with 5 c.c.

« ΠροηγούμενηΣυνέχεια »